Flooding is a Denial of Service (DoS) attack that is designed to bring a network or other service down due to large amount of traffic, hence the term “flooding”. These flood attacks occur when a network becomes overloaded with information, also known as packets, initiating incomplete connection requests that it can no longer process real connection requests. When an attacker floods the system with these requests that can’t be completed, it fills up the networks memory buffer. When the memory buffer is full of data, no other connections can be made to the network; causing a Denial of Service.
Source: Webopedia
Related Terms: Denial of Service (DoS), Distributed Denial of Service (DDoS)